The configuration of the combination of the availability check group (from material master) and check rule (default is normally 'PP') controls which stocks, receipts and issues are to be taken into account in MRP.

Please note, I would normally advise that QI stocks be taken into account as companies would normally expect material to be approved and you do not want to make additional product just because the goods are sitting in the quality department. You should only exclude QI stocks if the rejection rate exceeds 50% (i.e. you do NOT expect the product to be approved!) - You would normally control the USE of QI stocks by limiting the availability check on goods issue (e.g. check rule 'B', 'BO' etc) so that unapproved goods cannot be issued.

If you have product that cannot be used then they should be placed in something like blocked stock - as a default, this is normally excluded from the availability check.

If the problem is that the goods are still in QI when you are expecting to issue them to a sales order, then check your lead times and expecially the Goods Receipt Processing Time in the material master as this is supposed to include the lead time for quality inspection (i.e. it represents the time between completion of production and when stock is available for issue)